There is a demand for a mobile telephone to be further miniaturized and reduced in weight from the aspect of mobility enhancement. However, the extent to miniaturize operation keys is limited in consideration with operability. In addition, there is a demand for enlargement of the screen size in a main display. In order to make these opposing demands to be compatible from each other, a foldable mobile telephone has become a mainstream in recent years, in which a display case provided with a main display is connected to an operation case provided with operation keys by a hinge so as to be folded by mutually opposing a display panel including the main display and an operation panel including the operation keys.
There are various kinds of mobiles phones proposed, in which not only a first rotating axis for folding but also a two-axis hinge with a second rotating axis orthogonal to the first rotating axis are used to realize relative rotatability of the operation case and the display case using the second rotating axis as a center (ex. Patent Document 1). In such the mobile telephones, the cases can be folded by directing the display panel outward, so that the user also can browse the main display in a folded and miniaturized state.
However, in a reverse close state of being folded by directing the display panel outward, the operation panel is directed to the inside of the folded cases, so that it is impossible for the user to perform a key operation. Therefore, proposed is a conventional mobile telephone in which an operation input can be made in the reverse close state (ex. Patent Documents 2 and 3). Patent Document 2 discloses a mobile telephone provided with an operation input means on the display panel. Patent Document 3 discloses a mobile telephone provided with the operation input means in the side surface of the operation case.
Further, in a mobile telephone of recent years, a multifunction key capable of performing two or more different operation inputs corresponding to pressing portions is arranged on the operation panel. This kind of multifunction key is capable of performing four kinds of operation inputs of up, low, left and right in many cases, and called a direction key, a cross key or the like, which contributes miniaturization and operability enhancement of the operation panel (ex. Patent Document 4). Patent Document 4 discloses a mobile telephone provided with two multifunction keys, or more specifically a multifunction key operated in an expanded state of the cases and a multifunction key operated in a folded state.    Patent Document 1: Japanese Unexamined Patent Publication No. H11(1999)-30226    Patent Document 2: Japanese Unexamined Patent Publication No. 2001-251406    Patent Document 3: Japanese Unexamined Patent Publication No. 2002-33809    Patent Document 4: Japanese Unexamined Patent Publication No. 2002-118644